Field of the Invention
The present invention is related to the medical field and, more particularly, disposable syringes used in the medical field in which all or part of the syringe may be disposed of after a single use.
Description of Related Art
It is well known that syringes used in the medical field are typically disposable and are discarded after one use. These syringes usually comprise a barrel and a plunger mounted for reciprocal movement in the barrel, both parts usually being made of plastic material. Although disposable syringes are typically made by mass production methods such as injection molding, such disposable syringes are relatively expensive due to the materials and precision involved in their manufacture.
In order to reduce manufacturing costs, it has been proposed to combine a reusable syringe barrel and plunger with a replaceable container positioned either at the discharge end of the syringe barrel or within the syringe barrel. The container is typically flexible and acted upon by the action of the plunger to fill and dispense fluid from the container. For example, the container may be introverted or collapsed upon itself by action of the plunger to eject or administer a medicinal fluid contained in the container. An example of a syringe of this type is disclosed in U.S. Pat. Nos. 4,236,516 and 4,325,369 to Nilson. In the syringe disclosed in the foregoing patents, the container forms the end wall of the syringe barrel and comprises a substantially rigid first wall portion at the exterior side of the end wall and a flexible second wall portion at the interior side of the end wall. The container is introvertible upon the inside surface of the first wall portion. A nozzle is provided on the first wall portion for attachment of a hypodermic needle. In the Nilson syringe, as described in the foregoing patents, the container is formed as a spherical bulb having substantially the same diameter as the cylinder space formed by the syringe barrel. When an empty container is attached to the syringe barrel, the flexible second wall portion is introverted upon the inside surface of the first wall portion. To fill the container, the piston is withdrawn and the flexible wall portion is carried along by the piston due to sub-atmospheric pressure created between the piston and the flexible wall portion, while liquid such as blood or a medicinal fluid is pulled into the container. However, a substantial sub-atmospheric pressure (vacuum) is created by the piston during the latter part of the withdrawal stroke thereof, which requires considerable force to be applied to the piston at the end of the withdrawal stroke necessary for filling the container. Under certain circumstances, the container may not be completely filled.
U.S. Pat. No. 4,312,344 to Nilson seeks to overcome the foregoing deficiencies of the earlier Nilson syringes by providing a rigid spherical container that attaches to the end of the syringe barrel and has a collapsible spherical bulb attached thereto. This improved Nilson syringe further includes a plunger guided for axial movement in the syringe barrel, and a resilient plunger head connected to the plunger. The plunger has a diameter less than the diameter of the container but can be deformed to engage the spherical bulb when introverted upon the inside surface of the spherical container over substantially the entire surface thereof. The rigid spherical container attached to the end of the syringe barrel and the resilient plunger head on the plunger address some of the operational difficulties with the earlier Nilson syringes.
Other container-type syringes are known in the medical field which incorporate a bulb portion or bladder element such as may be found in U.S. Pat. No. 798,093 to Dean; U.S. Pat. No. 3,527,215 to De Witt; and U.S. Pat. No. 6,450,993 to Lin. The Dean patent discloses a syringe having a collapsible bulb portion secured to a glass container via a clamp. The bulb portion is in the form of a diaphragm/bladder that is secured to a cap portion. The De Witt patent discloses a bladder held within a cavity in a needle hub by a retaining ring. The Lin patent discloses a half-disposable syringe barrel including a reusable barrel syringe and a disposable cap member.
Moreover, syringes are known in the medical field that incorporate a collapsible container or bag that is breach-loaded into a syringe barrel and then acted upon by a syringe plunger inserted into the syringe barrel to expel the contents of the container. U.S. Pat. No. 2,690,179 to Fox and U.S. Pat. No. 3,166,070 to Everett disclose such container/bag-type syringes. The Everett patent discloses a dispensing syringe that includes a syringe casing, collapsible bag, and a plunger with a venting check valve in a passage in the plunger. The Fox patent discloses a collapsible container housed within a syringe housing and actuated by a plunger. The plunger includes an air passage in which a check valve is present to vent air from a forward side of the plunger head. The container is a sealed bag situated within a head portion of the housing and carries a needle assembly. Such container/bag syringes are also used in the blood collection area such as disclosed by U.S. Pat. No. 3,785,367 to Fortin et al. The Fortin patent discloses a rubber cup-shaped member that fits inside a rigid housing attached to a syringe barrel. The rigid housing includes a hollow tapered adapter supporting an arterial needle for collecting an arterial blood sample from a patient which enters a container provided within the syringe barrel under arterial blood pressure. The syringe barrel includes a reciprocal syringe plunger therein.